Method and means of electrolytic plating



sept. 23,1958

w. F. swAN-AroN METHOD AND OF ELECTROLYTIC PLATING Filed Nov. 18, 1955 A kh.

INVEN TOR. MLTE'R E SIYdNON w fh ATTDRHEY METHOD AND MEANS oF ELEcTRoLY'nc PLATING Walter F. Swanton, Avon, N. Y., assignor to Pfaudler Permutit Inc., Rochester, N. Y., a corporation of New York v Application November 18, 1955, Serial No.54`7,686

v 4 Claims. (Cl. 204-28) i lUnited States Patent O dissipate the heat generated by electrolytic action to maintain a proper operating temperature. Such plating processes include rst and second stagerinserbaths which gradually accumulate chromic acid concentration due to the articles being plated, carrying over some of the electrolyte, into the rinsing baths. In general, the rinse tanks are operated on a continuous overow basis, resulting in wastage and pollution, or the tanks are subjected to batch treatment to concentrate the chromic acid'laden wash water to plating strength for reuse. Such treatment has been accomplished by allowing concentration in the tirst rinse tank to build up during a days operation and distilling the contentsto 4bring the concentration to plating strength.

The present invention is directed to la system wherein the waste heat generated by electrolytic action is utilized to concentrate the plating solution by evaporation, whichevaporation is simultaneously effective to cool the solution. The water distilled in the process is used to establish a counterow through the rinsing tanks and into the plating tank whereby to substantially eliminate loss of electrolyte, and particularly for example, chromic acid or, i

such other metal of which the plating bath may be com# posed. The invention is further directed to a closed 'system wherein the electrolyte is continuously reconcen trated by distillation and the distilled water recovered and employed for rinsing. Further, the invention is directed to a system adapted for effective control to maintain a proper plating bath temperature without wastage of heat. l

The above and other novel features of the invention will appear more fullyhereinafter from the following detailed description when taken in conjunctionwith the accompanying drawing. It is expressly understood that the drawing is employed for purposes of illustration only and is not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

Referring to the drawing which shows a diagrammatic system and apparatus for carrying on the process, there is shown a plating bath 10, a iirst rinse bath 12, and a second rinse bath 14. Rinse water is supplied to the second rinse bath 14 through the rinse water supply pipe. 16. Rinse water is supplied to the first rinse bath by the syphon 18, flow being etfected when the level of the bath 1,2 is lower than the bath 14. In a similar fashion, the rinse water of the rst rinse bath 12 serves to supply make "ice .up water to the plating bath'10 through the syphon 20,

lthe first rinse bath and then into the second rinse bath 14 as indicated by the path of travel 15. While a certain amount of electrolyte is carried or dragged over into the first rinse bath, the concentration thereof is prevented from building up by reason of the continual counter-110W of such Abath into the plating tank, and similarly the second rinse is maintained substantially clear by introduction of distilled or make-up water and the continual counterliow into the irst rinse tank.

Initial heating of the electrolyte in the plating bath to operating temperature is accomplished, preparatory to commencing plating operation, by drawing olf electrolyte through the pipe 22, to the steam jacketed vessel 24, such jacket being indicated at 26. The electrolyte while being heated is recirculated to the bath 10 by the pump 28 which draws the electrolyte from the vessel 24 through the valve 30, and returns the electrolyte to the tank 10 through the open valve 32 and the return pipe 33. When the operating temperature of about 125 F. is reached in the plating bath, boiling will occur in the evacuated vessel and further temperature rise of the plating solution is thereby prevented.

It will be understood that the electrolytic action within the plating bath, during plating operations generates .considerable heat, and tends to raise the temperature of the bath above the temperature suitable for satisfactory operation. It is mandatory that such heat be dissipated. To maintain the bath at an optimum operating temperature of about 125 F., the vessel 24 is operated as a flash chamber or still at sub-atmospheric pressure, electrolyte being drawn into the still from the tank 10 through the pipe 22 and orifice or nozzle 23 by vacuum. The nozzle directs the incoming electrolyte toward the side wall of the vessel out of the path of rising vapor. A portion of the water is evaporated in the still, and the concentrated electrolyte remaining is drawn from the still and pumped to the plating bath through the return 33. The heat of vaporization cools the concentrated electrolyte remaining in the still, and thus on its return to the plating bath effects cooling thereof to maintain the operating temperature of 125 F.

Subatmospheric pressure to evacuate the system to a vacuum of about 26" of mercury is effected within the still by the vacuum source 36, which may be in the form of a steam jet exhauster. The boiling point within the still is thus lowered to about 125 F. Such vacuum source is conected through a condenser .to a centrifugal sepaf through the pipe 46, and pump 48 to the second rinsing tank 14, through the rinse water supply pipe 16.

The ash chamber or vessel 24 may be provided with temperature, vacuum and pressure gages 50, 52 and 54v respectively, and in addition is provided with a liquid level responsive control 56 for actuating the valve 32,

during the operation of the vessel 24 as a flash chamber or still, so that avproper liquid level may be maintained there within. Since but a part of the electrolyte drawn into the still is evaporated, the temperature of the elec trolyte in the bath, and circulating through the still, and being returned to the bath by the pump 23 will only vary by small temperature gradients, so that the tem-i' i perature of the liquid -leaving the still through the valve 3@ may be used for bath temperature control purposes as indicated at 31. The return temperature may therefore be utilized tocontrol'and vactua'te'the valve 39"f in the vacuum supply line 37,7atemperatureresponsecontrol 57 being provided. n

Thus` as temperature of the return increases at" "31, the valve 39 will be opened by the control S7 to incre'ase the vacuum in the still and increase the rateofivaporization ofthe electrolyte within the still. @vfhen the tem'- perature in the return decreases, the vacuum and rate' of evaporation willbe reduced. By so increasing vaporization, more heat o f vap-orization is removed from theelectrolyte in the still, and the temperature ofthel electrolyte returned to the platingbath is lowered thereby lowering the temperature of the/plating hath. An increase in temperature of the bathlwill result in an increased temperature within the still, and increase the rate of vaporization for a given vacuum, and increase the cooling effect thereof. An increase in vacuum, in response to an increase in temperature of the return liquid leaving the still, will increase the rate of ow of electrolyte into the still and increase the rate of-evaporation to effect lowering of the temperature of thefelectrolyte returned to the bath. Uuder such circumstances the liquid level control valve 32 will open wider and increase the rate or return to the plating bath, and thus increase the rate of circulation and cooling of the plating bath.

From the foregoing, it will be seen that the apparatus comprises a closed system, in which the water evaporated to provide the cooling effect, simultaneously concentrates the electrolyte for reuse. Such cooled electrolyte upon return to the bath is eiective to cool the bath to maintain the desired operating temperature. Thus the system requires additional water only to compensate for losses due to evaporation and decomposit-on in the plating bath, and such evaporation as may occur in the rinsing baths. The system requires only the addition of acid altes to bring the plating bath'to proper strength, and to compensate for metal lost by electrolytic `deposition in' the operation of the process, since, the electrolyte though weakened by the counterow from the'rinse tanks, is continuouslyreconcentrated and returned to the plating bath. The continuous counter'ow through the rinse tanks supplied by distilled water from the condenser maintains the rinse tanks effective, and at suciently low concentration to -lar reference to chrome plating itfwill be apparent lthat the system may be equally effective' in any electrolytic process wherein heat must be dissipated from the plating or anodizing bath to maintain an operating temperature and in which the plating or anodizing bath may be concentrated by evaporative apparatus simultaneously providing evaporative cooling, and in which the water thereby recovered is employed forreplenishing the rinsing baths. In some cases, rather than dilute the plating or anodizing bath by rinse water from the iirst rinse, the system may be so constituted as to separately withdraw solution from the plating bath and first rinse tank iny suitable proportions, before evaporating the withdrawn solutions,' which may be combined, in a common still. The recirculation of the plating solution through a still providing evaporative cooling to control the bath temperature, whereby such heat may be used to advantage instead of being wasted and-the recovery of electrolyte carried into'its running baths are outstanding features of the system.

Although a single embodiment of the invention has been illustrated and described, it is to be understood that the invention is not limited thereto. As various changes in the construction andarrangement or practice may be madewithoutfdeparting from the spirit of the invention, as will be apparent to those skilled in the art, reference will be had to the appended claims for a definition of the limits or the invention.

I'claim:

1. In an electrolyt'ic process wherein heat is generated during theelectrolyticy action occurring in an electrolytic bath and said bath is diluted by a stream of malte-up water, the method of controlling the temperature of the bath and concentrating the electrolyte which comprises the drawing of electrolyte from the bath, -maintaining'said`withdrawn electrolyte under sub-atmospheric pressure forevaporating'a' portion of the same forv concentrating and cooling the remainder, returning said cooled and concentrated electrolyte to said bath, and regulatingthe quantity of electrolyte withdrawn from said bath'and 'returned thereto in accordance with the temperature of the electrolyte in order to maintain the temperature of said bath within predetermined limits.

2. In an'electrolytic' process having washing means wherein heat is generated during the electrolytic action occurring in' an' electrolytic bath and said bath is diluted by flow from said washing means, the means of controlling the temperature ofv the bath and concentrating theV electrolyte which comprises the withdrawing of electrolyte from the bath, subjecting said withdrawn electrolyte to a partial vacuum forA evaporating a portion ofthe same' and cooling and concentrating the unevaporated p'o'rtion, `and returning the 'cooled and concentrated electrolyte" to said bath, and regulating the cooling and concentration of said electrolyte by controlling the vacuum' causing said evaporation in accordance with the temperature of the electrolyte Ain order to maintain the temperature of sa'id bath within predetermined limits.

3. In an electrolytic process in accordance with`claim 2 wherein` the vacuum causing said evaporation is controlled by 'temperature of said electrolyte and the volume of electrolyte withdraw-n and returned to said bath is controlled by said vacuum.

4.l In an electrolytic process comprising an electrolytic bath provided with a washing bath, the method of controlling the ltemperature of the electrolytic bath, concentrating the electrolyte and maintaining the purity of the Washing` bath comprising the steps of withdrawing electrolyte from said electrolytic bath, subjecting said Withdrawn electrolyte to a partial vacuum for evaporating 'a portion thereof and cooling, and concentratingI the unev'apor'ated portion, Yreturning the cooled, concentrated electrolyte to s'aid electrolytic bath, condensing the vapors from the evaporated .liquid and returning the condensate to 'said washing bath, allowing said Washing bath to counterow into said electrolytic bath, and regulating the cooling and concentration of said electrolyte by regulating the rate of evaporation and the quantity of elec-V trolyte withdrawn from said electrolytic bath and returned thereto by regulating said vacuum in accordance with the temperature Vof said electrolyte, in order to maintain the temperature of said electrolytic bath within predetermined limits.

References Cited in the rile of this patent UNITED STATES PATENTS 2,185,095 Smith et al. a- Dec. 26, 1939 2,433,441 DaVdOl Dec. 30, 1947 2,626,621 Curtis Jan. 27, 1953 2,721,562 Irvine Oct. 25, 1955 

1. IN AN ELECTROLYTIC PROCESS WHEREIN HEAT IS GENERATED DURING THE ELECTROLYTIC ACTION OCCURING IN AN ELECTROLYTIC BATH AND SAID BATH IS DILUTED BY A STREAM OF MAKE-UP WATER, THE METHOD OF CONTROLLING THE TEMPERATURE OF THE BATH AND CONCENTRATING THE ELECTROLYTE WHICH COMPRISES THE DRAWING OF ELECTROLYTE FROM THE BATH, MAINTAINING SAID WITHDRAWN ELECTROLYTE UNDER SUB-ATMOSPHERIC PRESSURE FOR EVAPORATING A PORTION OF THE SAME FOR CONCENTRATING AND COOLING THE REMAINDER, RETURNING SAID COOLED AND CONCENTRATED ELECTROLYTE TO SAID BATH, AND REGULATING THE QUANTITY OF ELECTROLYTE WITHDRAWN FROM SAID BATH AND RETURNED THERETO IN ACCORDANCE WITH THE TEMPERATURE OF THE ELECTROLYTE IN ORDER TO MAINTAIN THE TEMPERATURE OF SAID BATH WITHIN PREDETERMINED LIMITS. 